A deep vein thrombosis (DVT) is a blood clot, or thrombus, that forms in a vein. A principal risk of a DVT is that it will embolize and become a life-threatening pulmonary embolism (PE). The disease process venous thromboembolism (abbreviated as VTE or DVT/PE) can refer to DVT and/or PE. The accepted standard of care for patients with DVT is anticoagulant therapy. Inferior vena cava (IVC) filters are typically reserved for those patients who fail anticoagulant therapy, or have a complication or contraindication to anticoagulant therapy. In some cases, both anticoagulant therapy and an IVC filter may be used to treat patients with DVT.
An IVC filter is deployed in the vena cava to capture thrombotic or embolic material before it can cause a PE. The filter may be deployed permanently, or as a temporary IVC filter that may be retrieved after a period of time. A temporary IVC filter may be deployed while thrombolytic medication is administered to reduce the thrombus. The temporary IVC filter would capture any parts of the thrombus that might come loose while the thrombolytic medication is administered. After a period of time, the risk of a PE may be lessened and the filter may be retrieved.
The use of an IVC filter, particularly a temporary IVC filter, may require periodic monitoring to detect whether and to what extent thrombotic material is captured by the IVC filter. As the IVC filter captures thrombotic material, the filter may become burdened with so much thrombotic material that it forms an obstacle for blood flow to the heart. An overly burdened temporary IVC filter may also be filled with enough thrombotic material to affect the collapsibility of the filter making the filter more difficult to retrieve, increasing the risk of dislodging the thrombotic material and causing a PE. Prior to retrieval, thrombus captured in an overly-burdened filter may be treated to reduce the size of the thrombotic material. Treatment may be by chemical means, such as by administration of a thrombolytic agent, by mechanical means, such as by employing a structure that mechanically disrupts the thrombotic material, by pressure such as pressurized fluid injection or sonication of the thrombus or by thermal means, such as by laser or other energetic means for disrupting the thrombus. It will be understood that the foregoing means for treating the thrombus captured in the IVC filter are exemplary only and non-limiting. Alternative means for treating or reducing the thrombus captured within the IVC filter as may be currently or hereinafter known in the art are also contemplated by the present invention. Under all circumstances, however, prior to removing a temporary IVC filter, it is highly desirable to detect both the presence of thrombus in the filter and evaluate its size and effect on withdrawing the temporary IVC filter while controlling the risk of pulmonary embolism as a result of thrombotic material being released from the temporary IVC filter during retrieval.
Known methods of detecting the presence of a thrombus in an IVC filter rely on the use of expensive imaging processes and medical imaging equipment. When it is desired to determine if a thrombus is present in an IVC filter deployed in a patient, the patient is typically moved to an imaging facility. The area in which the filter is deployed in the patient's body is imaged. If the imaging is performed using x-rays, the imaging generates cavograms or angiograms, which are then analyzed to determine if a thrombus is present in the filter. Other such imaging methods include intravascular ultrasound (“IVUS”), venography, and CT scans.
It would be desirable to be able to determine at the patient's bedside whether a thrombus is present in the IVC filter without the need for imaging, or to make preliminary determinations of the presence of a thrombus in the IVC filter prior to imaging to quantify the presence and size of the thrombus.